Too many things wrong with these comparisons. Let's look at ShadowFall - it's poised to overtake KZ3 - and launched on a FAR lower userbase. No new Halo has released, so that's irrelvant. The "brilliance of Uncharted" and what's in your collection is also moot. Wii Sports - um, nobody suggested that Uncharted 4 would sell like it (not sure how such a comparison even makes sense when speaking even figuratively).
Bottom line, install bases grow with new releases, especially from acclaimed series'. Thus, saying it will sell 6 million max is low balling the game.
The thing is: I don´t really know man, i just gave my opinion. I am no expert. heck, I barelly can speak english. 6 million sounded good to me, but, well, the more, the merrier; 10 million, 20 million... Naughty dog sure deserves it...
I talked about my collection because I thought that you treating me like a uncharted hater or something... Clearly not the case, just see my trophy collection, it is all there.